Hi all Have on old os 60 sr that requires a new piston ring, The engine has a bore size of 24mm, and the ring has a locating grove at the rear. Looked at the discontinued engines on the os site and this engine is not listed. On reading a thread on an other site on other side of the pond the .61 sf only has a bore of 22mm. The other size 60 engines on the os site have a piston rings with no grove. Does anybody know where i could get one from or has one ?